/**
 * @license
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import '../../../styles/shared-styles.js';
import {GestureEventListeners} from '@polymer/polymer/lib/mixins/gesture-event-listeners.js';
import {LegacyElementMixin} from '@polymer/polymer/lib/legacy/legacy-element-mixin.js';
import {PolymerElement} from '@polymer/polymer/polymer-element.js';
import {htmlTemplate} from './gr-page-nav_html.js';

/** @extends PolymerElement */
class GrPageNav extends GestureEventListeners(
    LegacyElementMixin(
        PolymerElement)) {
  static get template() { return htmlTemplate; }

  static get is() { return 'gr-page-nav'; }

  static get properties() {
    return {
      _headerHeight: Number,
    };
  }

  /** @override */
  attached() {
    super.attached();
    this.listen(window, 'scroll', '_handleBodyScroll');
  }

  /** @override */
  detached() {
    super.detached();
    this.unlisten(window, 'scroll', '_handleBodyScroll');
  }

  _handleBodyScroll() {
    if (this._headerHeight === undefined) {
      let top = this._getOffsetTop(this);
      for (let offsetParent = this.offsetParent;
        offsetParent;
        offsetParent = this._getOffsetParent(offsetParent)) {
        top += this._getOffsetTop(offsetParent);
      }
      this._headerHeight = top;
    }

    this.$.nav.classList.toggle('pinned',
        this._getScrollY() >= this._headerHeight);
  }

  /* Functions used for test purposes */
  _getOffsetParent(element) {
    if (!element || !element.offsetParent) { return ''; }
    return element.offsetParent;
  }

  _getOffsetTop(element) {
    return element.offsetTop;
  }

  _getScrollY() {
    return window.scrollY;
  }
}

customElements.define(GrPageNav.is, GrPageNav);
